Former King of the Crystal Empire Sombra wakes up in a cell with the given decision between reformation or a lifetime in prison. He accepts with some caution and after some details are sorted out, he is moved to the castle of Princess Twilight Sparkle under reformation.
With all the craziness about the arrival of an evil slave king going through the humble town of Ponyville, Sombra is left wondering what he got himself into.
Can two ponies who hate each other with all their guts become friends and prove that old habits can be changed? It depends on how you define 'hate'...

UPDATE: Under... construction perhaps? It has been years but... maybe I'll update this. After I rewrite every chapter, of course.